A proximity sensor for measuring the distance from a target contains a microwave oscillator providing a transmission wave output signal emitted toward the target as a free space transmission wave which is reflected by an electrically conductive target surface as a free space reflection wave received by the proximity sensor as a reflection wave. The distance is determined from the transmission wave and the reflection wave. The transmission wave is guided in a waveguide transmission path as a waveguide transmission wave. The transmission wave is coupled into the waveguide with a wave mode leading to the detachment of the waveguide transmission wave at the waveguide front end aperture into the free space transmission wave and to the propagation of the free space transmission wave to the target. At least one reception path is electromagnetically decoupled from the transmission path and guides the reflection wave as a waveguide reflection wave.